1. Field of the Invention
This invention relates to an outboard motor steering system and more specifically to an outboard motor steering system wherein the steering mechanism is driven by an actuator.
2. Description of the Related Art
The source of motive power for conventional outboard motor steering mechanisms including, for example, the tiller handle type, where a tiller handle mounted to the outboard motor is steered by an operator's hand, and the remote control type, where the steering mechanism is controlled remotely via a push-pull cable, is generally human power.
However, the steering load is typically heavy in such systems that utilize human power, so the burden on the operator is large. To solve this problem, for example, with the prior art recited in Japanese Laid-Open Patent Application No. Sho 62(1987)-125996, FIG. 2, etc., a hydraulic actuator (specifically a hydraulic cylinder) is connected to the steering mechanism (tiller handle) of the outboard motor via an arm and the like, thus reducing the steering load by actuating the hydraulic cylinder in a manner corresponding to the steering input of the operator. A pump that supplies hydraulic fluid to the hydraulic cylinder is connected to a steering wheel, and the hydraulic cylinder and pump are connected via hydraulic lines disposed within the hull (boat).
In addition, prior art that allows the tilt and trim angles of the outboard motor to be adjustable with a hydraulic actuator has also been proposed by, for example, Japanese Laid-Open Patent Application No. Hei 7(1995)-228296, FIGS. 2, 3 etc.
However, with the prior art recited in '996 mentioned above, where the mechanism for supplying hydraulic fluid to the cylinder (i.e., pumps and hydraulic paths) is disposed in the boat, there are problems in that the structure becomes complex and the number of parts increases, and also the work of installing the system in the boat becomes complicated.
Further, when the steering angle of an outboard motor is adjusted with a hydraulic actuator, this requires a hydraulic fluid supply source (hydraulic pump and electric motor that drives the hydraulic pump) for supplying fluid to the actuator. However, the steering load of an outboard motor (specifically, the driving force of the hydraulic actuator required to adjust the steering angle) varies greatly depending on the type of boat, its speed, the wave conditions and the like. Accordingly, if the output torque of the electric motor that drives the hydraulic pump is inadequate, differences in the driven speed of the hydraulic actuator arise depending on fluctuations in load, so there is a risk of deterioration of the steering feel.
To solve this problem, the electric motor that drives the hydraulic pump is typically given sufficient output torque to be able to adequately handle the maximum hypothetical load so that stable steering can be achieved even should fluctuations in the steering load arise. However, with such a configuration, there is a problem in that torque that exceeds the output required for steering continues to be provided as output even at times of low loads, so the operating efficiency is poor and the power consumption is wasteful.
Furthermore, when the tilt and trim angles of an outboard motor are adjusted using a hydraulic actuator, a hydraulic fluid supply source for supplying fluid to this actuator is also required and the required capacity of this hydraulic fluid supply source to supply pressurized hydraulic fluid also varies greatly depending on the load factors of the type of boat, its speed and the wave conditions.
Specifically, there is a problem in that in order to stably adjust the tilt and trim angles with a hydraulic actuator, it is necessary to avoid increasing the power consumption by the hydraulic fluid supply source in the same manner as for steering.